The invention relates to a polarizer for electromagnetic radiation, wherein the polarizer has electrical conductive elements arranged in parallel and in specific distances to one another.
In order to obtain a dual circular right or left polarized electromagnetic wave, planar polarizers that are situated above the radiating antenna opening are used for planar antennas that are arranged as dual linear polarized antennas.
The polarizer breaks up the E-vector of an impinging wave into two orthogonal components and produces a phase difference [spacing phase] of xc2x190 degrees between the components and which, with subsequent overlay, results in a circular polarization. The mode of action likewise applies to the conversion of a circular into a linear polarization.
Two constructively different types of polarization are known. The one type of polarization uses several Polarization structures arranged in an interval of xcex/4 (quarter lambda) that act on the one hand inductively and on the other hand capacitatively on the respective E-field components and thus produce the phase difference. These polarization structures are often carried out as etched complex folded line circuits on a matrix (foil). In this situation at least two such structures (inductive, capacitative) are required for a polarizer. The required witch or spacing is created by the use of a low dielectric material. The disadvantage in this embodiment is its high sensitivity to engineering tolerances. Likewise, good flatness and very precise positioning of the foils used must be assured. This frequently leads to additional expense in the form of positioning guides for gluing and bonding and where [com]pression of the layers is required.
Another polarization type also uses electrically conductive elements in the form of metal struts [sic] which are arranged at a 45 degree angle to the linear polarization. Due to the different electrical constraints two different field types form and are expanded by the polarizer. Due to the different propagation times a phase difference of xc2x190 degrees is produced at the output of the polarizer at superpositioning of these phase types and, consequently, a right or left circular wave is produced. The electrical characteristics are determined by the spacing of the metal struts relative to one another and their length in the principal direction of antenna radiation. The metal struts are enclosed in a metal frame and their ends are either bonded or soldered to the frame. The advantage of this type of polarizer is the electrical simplicity and the satisfactory electrical characteristics such as, for example, large frequency bandwidth, relative insensitivity to engineering tolerances, very low insertion loss, very good elliptical [wave] values and adaptation. The disadvantage in this polarizer type is the costly and consequently the expensive fastenings of the metal struts to the frame, since either two bonding- or soldering steps are involved for each metal strut. Moreover, frequently metal stresses are created that are caused by the engineering tolerances at the time of manufacturing the metal struts and when inserting the metal struts into the mounting frame. The mounting frame weight is disproportionally high, since it is most often made of metal.
The purpose of the present invention is, therefore, to provide a polarizer that is simple in construction and economical to manufacture.
The solution to this problem presented on the one hand by a polarizer of the type described earlier and pursuant to the invention in which the elements are held in position by at least one spacer element, wherein each spacer element is made of a low dielectric material. A further solution is offered if the elements are removably or unremovably inserted into a board or strip shaped spacer and are held in position relative to one another by at least one spacer element.
In the polarizer described in the invention the mounting frame is eliminated completely. By doing so, the weight of the polarizer is advantageously reduced. The positioning of the conductive elements which are most frequently fashioned from metal struts or metal strips is achieved by the spacer made of a particularly low dielectric material. Since the recesses provided for accepting the conductive elements are milled, etched or otherwise produced at the same time in the form of grooves, slots or bore holes in the low dielectric material, the spacing and the width or pitch of the grooves or slots relative to one another is always the same and is subject to only low engineering tolerances. This solution represents an essential improvement of the electrical characteristics of the polarizer.
Polystyrol in its foam form, for example, is suitable as the low dielectric material.
It is advantageous to realize the grooves or slots, that are arranged at a 45 degree angle to the linear polarization, somewhat narrower than the conductive elements to assure that the conductive elements do not fall out of the spacer element. By inserting the conductive elements into the grooves or slots the side walls of the slots are pushed apart whereby a compression force is produced which prevents the elements from falling out of the slots. However, this procedure can also result in the occurrence of very high tensions in the spacer that is preferably constructed as a plate or strip. These tensions can be reduced or completely eliminated if additional recesses are provided in the spacer. Said recesses can be placed on the side containing the grooves or slots and/or on the side opposite to same. In this manner, the material that is displaced by the inserted conductive elements can expand without the occurrence of internal stresses within the spacer that would tend to deform it [lit. to xe2x80x9cbendxe2x80x9d it]. The supplemental recesses can, for example, also be grooves or slots. The shape of the recesses is optional and can be adapted to local requirements.
In order to prevent the metal struts from falling out as conductive elements there is the additional possibility of covering or enveloping the polarizer with the same low dielectric material used in the spacer. This can be done by a bonding process or by coating, application of a foam, or foaming over the surfaces of the grooves or slots.
It is also possible to bond the elements together with the spacer element. In a further advantageous embodiment of the invention the conductive elements do not rest in grooves or slots, but in bore holes into the low dielectric material. Depending on the cross-sectional shape of the conductive elements the borings can be replaced by the recesses adapted to that shape.
The conductive elements can be advantageously prevented from falling out of the grooves or slots in that the depth of the grooves or slots may be larger than the height of the conductive elements in such a manner that each groove or slot together with the element situated in it can be filled or covered with a sealant or filler material and preferably done to be flush with the surface of the spacer element. In this way a flat surface of the polarizer is made possible whereby at the same time the conductive elements are protected from corrosion.
The necessary spacing between the antenna and the conductive elements of the polarizer can be integrated into the overall level of the low dielectric material.
In order to fasten the polarizer to a planar [flat, bedspring] antenna it is sufficient that the already existing external edges of the planar antenna housing be extended and after placement of the polarizer on the antenna it be folded over it so that the polarizer forms a unit with the antenna.
A further advantageous embodiment of the polarizer would be if the interspaces between the conductive elements were partially or completely filled with a low dielectric material. The low dielectric material The low dielectric material can, but does not have to be, the same low dielectric material as that used in the spacer element. It can be pushed in or filled in between the elements at a later time, for example, by a expanding foam-fill process. Inasmuch as the polarizer is of such design that the interspaces between the conductive elements is not filled in, the interspaces need not necessarily be filled in with a low dielectric material. The decision depends essentially on the stability and the electrical characteristics of the polarizer in conjunction with the planar antenna.
In order to assure that the polarizer and the associated flat or planar antenna are constantly in the correct positional relationship to one another, they can, as already described above, be enclosed in a casing or a housing. It is also possible to bond the flat antenna to the polarizer. Furthermore, it is possible the polarizer and the flat antenna and hold them in a position relative to one another by surrounding or imbedding them using a preferably low dielectric material. By surrounding them with foam or imbedding the two components, the two components are advantageously hermetically isolated from the environment so that they are optimally protected from mechanical or atmospheric related influences.
Furthermore, the purpose of the present invention is to provide a method for manufacturing the polarizer described in the invention by means of which the polarizer can be manufactured in the fewest steps and most economically.
This purpose is clearly accomplished in that, first of all, in the spacing element, of which there is at least on and which is made out of a particularly low dielectric material, recesses but especially grooves or slots or borings are milled, etched, cut, sawed, burnt, bored or pressed and then the elements are then inserted, bonded, or compressed into the grooves or slots. It is thus possible to introduce or to insert the elements sequentially or individually into the spacer element.
Inasmuch as there are not recesses for the conductive elements in the spacer element, it is possible to simply impress the elements into the material of the spacer element. When doing this, however, often considerable stresses occur in the material itself, since a relatively large quantity of the material is displaced by the elements. If the conductive elements are properly heated it is possible to bring the material of the spacer element, which is advantageously polystyrol, to melting or burning so that the elements can be impressed into the material of the spacer element with relatively little force, whereby simultaneously hardly any stresses occur in the material of the spacer element.
Depending on the type and the form of the spacer element, the interspaces between the elements after their insertion may not yet be filled in. Said interspaces can then be filled in or foamed in with low dielectric material. It is nonetheless also to insert precisely fitted preformed elements made of low dielectric material into the interspaces so that the interspaces are completely filled.
The manufacture of the polarizer as described in the invention can also be accomplished in that the conductive elements are held in parallel and in the correct spacing to one another and then imbedded or foamed in with a particularly low dielectric material. It is also useful and feasible to arrange the elements in the correct spacing intervals relative to one another and to the flat antenna to imbed or to foam in the elements together with the flat antenna using a suitable material. In this instance the flat antenna does not necessarily have to be included in the integration. It is also possible to produce the polarizer separately from the flat antenna by an imbedding or foaming-in process.